As a method of estimating a network bandwidth between terminals, there is a method of actively diagnosing traffic of a network (hereinafter referred to as “active diagnosis”) and a method of passively diagnosing traffic of a network (hereinafter referred to as “passive diagnosis”). In the active diagnosis, a diagnosis device measures a network bandwidth by flowing packets having a network bandwidth diagnosis pattern that has been prepared beforehand through the network. Thus, there are problems that a diagnosis pattern has to be prepared and packets that are not desired for the network flow through the network.
In the passive diagnosis, it is assumed that all packets that flow through the network are measurement targets. As the passive diagnosis, a technology is known in which a packet that arrives at a path is captured in which packets that are monitoring targets are collected, and a communication quality of a client is analyzed for each location based on location information of the client in each of the packets, for each connection. As a related art, for example, Japanese Laid-open Patent Publication No. 2003-258881, Japanese Laid-open Patent Publication No. 2012-191440, and the like are disclosed.
However, in the passive diagnosis, there is a problem that it is difficult to measure an accurate bandwidth of the network. This problem, that is, the difficulty of measuring an accurate bandwidth of the network is described below.
Continuous packets that are suitable for measurement of a bandwidth may not typically flow through the network. The terminal on the network performs flow control in which packets are transmitted at intervals in order to avoid congestion of the network. Therefore, measurement of an accurate bandwidth may be achieved by removing a packet the transmission of which is delayed by the flow control.
Generally, it is probable that a packet that is transmitted immediately after an acknowledge packet (ACK) has been received from among packets that are continuously transmitted from the terminal is generally affected by the flow control. However, it is difficult to identify a packet that is transmitted immediately after an ACK has been received, at an observation point, due to a time difference of transmission/reception of the packet between the terminal, and the observation point between terminals. FIG. 21 is a diagram illustrating deviation between transmission timing of a terminal and reception timing of an observation point.
As illustrated in FIG. 21, in a packet analysis device at the observation point, packets that are received between ACKs may not correspond to continuous packets that has been continuously transmitted from the terminal. Here, in the packet analysis device, data packets that are received at the times of “d1” and “d2” correspond to continuous packets, and data packets that are received at the times of “d3” and “d4” correspond to continuous packets. After that, the packet analysis device receives data packets at the times of “d2” and “d3” between an ACK that is received at the time of “a1” and an ACK that is received at the time of “a2”. Thus, packets that are received between ACKs may not correspond to continuous packets.
The packet analysis device at the observation point may not receive a data packet that corresponds to an ACK immediately after the ACK has been received. Here, the packet analysis device receives an ACK at the time of “a1”, and receives a data packet that corresponds to the received ACK, at the time of “d3”. The packet analysis device receives continuous packets that correspond to a further ACK, at the time of “d2” immediately after the ACK at the time of a1 has been received. Thus, the packet analysis device may not receive a data packet that corresponds to an ACK immediately after the ACK has been received. That is, at the observation point, it is difficult to identify a packet that has been affected by the flow control.